Retaining walls for terracing
For a landscape with a slope, it is most rational to terracing the site. Simply put, to equip a stepped relief, where each horizontal platform is supported by a retaining wall.
Those who built a house with their own hands know that ground pressure acts on the foundation from the outside — the same story with retaining structures. In winter, the matter is complicated by heaving (expansion, due to freezing of moisture drops) of the soil. In order for the design of the retaining wall to be resistant to such an impact, there are several rules for its construction.
The location of retaining walls should be designed in such a way that the earth would be poured into them, and not taken out.
- Firstlythe top layer of soil is more stable, and in the lower layers it will settle under the weight of the wall material.
- Secondlythe back of the retaining structure will be free to form a drainage system.
- Thirdlythis is the least expensive option without the involvement of earthmoving equipment.
FOUNDATION CALCULATION. For retaining walls, whose height does not exceed 30 cm, it makes no sense to build a foundation — you can limit yourself to crushed stone bedding buried in a trench (10-15 cm). In other cases, the depth of its occurrence and the width of the sole directly depend on the height of the wall and the characteristics of the soil. In order not to complicate the calculations, we give the following constants:
- Depth strip foundation on non-rocky soils for retaining walls from 30 to 80 cm is 30 cm, increasing the height from 80 to 150 cm entails deepening the foundation to 60 cm. On heaving soils, this value is compared with the depth of soil freezing.
- Foundation base width must exceed the width of the base of the wall by at least 15-20 cm, this will ensure the stability of the entire structure during operation.
The wall itself (body) during operation will withstand certain loads and may eventually deform under the pressure of the soil.
In order to prevent such a process, the body of the retaining wall, if its height exceeds 1.5 m, together with the foundation, is usually made with a slight slope towards the terrace.
The strength of the structure will increase significantly if the wall line on the plan has smooth bends (it will not be straight).
- longitudinal drainage — gravel or sand backfill and a perforated drainage pipe laid at the base of the foundation on the back of the wall;
- transverse drainage — a pipe laid across the wall body in order to drain the runoff to the outside, the frequency of pipe laying depends on the height of the retaining wall (read further in the article).
Do not neglect this rule — and your work, as well as the invested funds, will not be wasted.
Without drainage on non-porous soils, only structures with low (up to 60 cm) “movable walls” can be made (dry masonry, log walls, ready-made modules, where water flow comes from drainage backfill and holes between body elements. But even in this case, gravel is required The drainage system, together with the crushed stone cushion, is protected from the penetration of soil and the germination of the roots of herbaceous plants with geotextiles.
Armed with basic knowledge, you can begin to familiarize yourself with the types of retaining walls available for self-execution.
The most decorative and spectacular type of retaining structure is a wall made of natural stone (sandstone, dolmite). There are two methods for laying this natural material: dry and mortar.
For DRY MASONRY only those types of stone are suitable that, when chipped or sawn, form relatively flat surfaces.
The strength of this design is supported by its weight, the slope of the front wall and the necessarily uneven surface of the back.
The recommended maximum masonry height is 80 cm.
The most massive stones are laid in its lower part, always in a checkerboard pattern, the voids are filled with small ones and sprinkled with a cement-sand mixture.
The slope of the front wall is about 60the width of the wall at the top is at least 45 cm, but for different types of soils, these figures may vary. On clay soils, the thickness of the base should be at least a quarter of the height of the body. For loose (sandy) and wet soils, this figure increases to half the height, respectively, and the width of the top of the wall increases.
For walls of greater height or in order to save material, it is used RIGID STRUCTUREfixed on a cement-lime mortar.
To give more decorative effect, different-sized elements are involved in the masonry, including inclusions of individual large stones.
The slope of the outer plane of the wall is up to 120provided that its height together with the foundation is more than 1.5 m. for lower heights, the stone retaining wall is made the same in width.
The drainage system should be provided in any case: crushed stone filling must be combined with a drainage system, and it consists not only of a pipe laid at the base, but also of plastic pipe segments embedded in the wall at a height of about 5 cm from the base perpendicular to the foundation line and with a slight slope.
The frequency of laying transverse drainage is 1 m with a wall height of 1.5 m, the lower the height (soil thickness), the less often drainage is laid.
The advantage of monolithic structures of retaining walls is that there is no need to deeply deepen the foundation — its sole goes into the ground to a depth of 15-25 cm.
Among other things, you have a great opportunity to clad the wall with any kind of facade tiles. With a height of up to 1.5 m, together with the foundation, the thickness of the monolithic retaining wall can be uniform. Gravel bedding is done no more than 10 cm and carefully compacted. The sole of the foundation in this case is three times wider than the wall and extends away from the terrace, forming a letter L.
Great height requires the formation of a slope of the front wall up to 100. By the way, its appearance from this only improves, as the sun’s rays glide along such a wall, hiding flaws in the finish. The width of the base of the foundation is three times the thickness of the wall in its upper part.
Transverse drainage (pipes across the body of the wall) are laid in the base, going beyond the boundaries of the formwork with the same frequency as for the stone wall. As for the formwork, its installation begins from the back wall: first, stakes are driven in behind the foundation, leaving room for the formwork and going into the ground a third of the height (otherwise they will not withstand the pressure of concrete), then the back wall is formed. The next step is the installation of the front wall: vertical pillars cannot be driven into the foundation, therefore, the formwork sheathed from the inside with roofing material (to obtain a smooth surface) is fixed with oblique stops at several height levels.
There are two casting options for monolithic execution: REINFORCED CONCRETE and rubble concrete. For the first, a sufficient minimum wall thickness is 15 cm, for the second, 25 cm. As a reinforcing material, two rows of metal mesh, trimmings of reinforcement or pipes, fastened together with wire, are suitable. In order to avoid shifting of the outer formwork, concrete pouring (grade M-100) is carried out level by level.
Very convenient option FIXED FORMWORK — ready-made hollow blocks are laid out on top of each other in a checkerboard pattern, reinforced with reinforcement and poured with concrete.
- large stones are laid dry in the lower row,
- crushed stone is poured into the voids, transverse drainage is fixed between them,
- a row is poured, but the stones are not completely covered with concrete, leaving 3-4 cm for adhesion to the next row,
- then again a row of rubble, crushed stone backfill and pouring.
At one time, you can pour as much mortar as you have available, the main thing is that the upper row of stones be laid out across the entire width of the wall, and the lower part of the buta should be sunk into concrete. When resuming work, the top of the masonry is moistened with water.
Concrete in the formwork «freezes» for at least 3 days, and the working load on the wall is allowed no earlier than a month later. The technological break can be filled with wall cladding. Drainage is done according to the general scheme, diverting water into a sump with subsequent use for irrigation.
A log wall is a rather economical option, but short-lived and is done with the expectation of renewal in 5-10 years.
The exception is larch, which only grows stronger from exposure to moisture. Although, in the areas of the steppe zone, it can hardly be called an economy option.
When choosing log sizes, the following ratio is used: the length of the workpiece is one and a half times the visible part (wall height), and the diameter is 10% of the length of the workpiece.
Let’s say the height of the retaining wall of logs is 90 cm (higher — economically unjustified). Then it is necessary to select logs with a length of 135 cm (90 x 1.5) and a diameter of about 14 cm. The method of laying the wall is pile.
First of all, they dig a trench three times the width of the log along the line of laying the retaining wall. Its bottom is carefully rammed, a gravel cushion of 5-10 cm is laid and rammed again. The lower third of the blanks is freed from the bark and impregnated with hot drying oil, bitumen or fired, the upper one is treated with a colorless antiseptic.
The trunks are placed in a strictly vertical position, sprinkled with gravel from below. They pour concrete of the M-100 brand and allow the solution to stand for at least a week.
Drainage is done according to the general scheme, with a low wall height — without a drainage pipe (it is enough to have gaps between the logs).
For a brick retaining wall up to 1 m high, the option of laying on a cement-sand mortar one brick thick is suitable.
The second row is done with vertical gaps through every fourth brick: just do not fill the side gaps with mortar — these are drainage holes.
If the retaining structure is made for the purpose of arranging earthen terraces, the wall thickness is increased to one and a half bricks.
As they are laid, until the cement has hardened, jointing joints are formed: it is better to make them convex or flush with the plane of the wall, but not recessed (over time, the strength of the structure may be impaired).
Avoid even and long brick walls: bends, curvilinear and uneven levels make the retaining wall more stable.
Both clinker and ordinary baked clay bricks are used in masonry. The voids in the structural elements can be torn apart by moisture accumulated in them in winter — therefore, use only full-bodied masonry material. The presence of drainage holes does not replace the construction of a full drainage system behind a brick retaining wall — take care of drainage.
WALL OF HOLLOW BLOCKS AND GABIONS
Ready-made modules will help speed up the installation of retaining walls.
The choice today among such products is not so great, but manufacturers offer interesting options: from fixed formwork, which can be decorated at your discretion, to curly shaped elements stacked on top of each other in a checkerboard pattern and gabions.
The cavities of the modules are filled with crushed stone or soil, turning them into containers for vertical gardening. From the same hollow blocks, you can mount a monolith based on fixed formwork, as read above (in the MONOLITHIC WALL section).
Retaining walls are far from being an independent element of a yard or garden. Any transition from one level of the terrace to another must be equipped with steps.
Most often, such stair passages are made of the same materials as the wall itself.
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